Smart devices are often used in a low lighting environment in daily life. The light emitted from a backlight of an smart device may be harsh on a user's eyes when the ambient light is weak, so the user will turn down the brightness of the backlight, such that the backlight of the smart device will emit light with lower brightness to adapt to the environment. However, even if the brightness of the backlight of the smart device has been adjusted to a minimum brightness, the user may still feel harsh when using the smart device in a dark place.
In the related art, the current provided by a control chip of a terminal device to the backlight is in direct proportion to the brightness of the backlight, so the current supplied to the backlight of the smart device is decreased in order to gain a lower brightness. However, if the brightness of the backlight is turned down only by reducing the current supplied to the backlight, the signal-noise ratio of the control chip for providing current to the backlight is rather low when the current supplied to the backlight is reduced to a certain extent, such that the control chip is considerably influenced by external noise. Consequently, when the user sets a fixed ultralow brightness for the smart device, the control chip of the smart device may be subject to external noise interference, and hence the current outputted from the control chip to the backlight may be unstable. When the backlight receives an unstable current supply, the brightness of the backlight flickers as the current outputted from the control chip varies, and thus the backlight cannot be kept at a fixed low brightness. Flickering of the backlight of the smart device at a low brightness not only degrades user experiences, but also reduces the life of the backlight due to current instability.